White & Williams Chairman and Managing Partner Guy Cellucci died on Friday, the firm said. He was 59.

Mr. Cellucci had been at the helm of the Philadelphia-based law firm since October 2010, when he succeeded George Hartnett. During his tenure as chairman and managing partner, White & Williams grew in size, breadth and practice offerings. The firm doubled the size of both its New York and Boston offices.

“He did not force his ideas on others, but listened to what they had to say and formulated a plan of action after forging consensus in a way that only a great leader can do,” said Patricia Santelle, chair of the firm’s commercial litigation department and Mr. Cellucci’s close friend. “He was a friend, mentor and partner in every sense of the word.”

Former Pennsylvania Bar Association President and White & Williams partner Andrew Susko, said of Cellucci: “He brought professional excellence and integrity to everything he did for this firm and he will be deeply missed.”

White & Williams said its executive committee met Saturday. The firm’s executive director, Ken Gibb, will lead the firm administratively until a new chairman is named, per the firm’s partnership agreement. At this time, the firm said it is focusing all of its attention on supporting Mr. Cellucci’s family and firm matters will not be discussed until after his funeral.

“Guy was an outstanding leader and has left the firm in good working order,” Gibb said. “We will continue with the leadership that Guy put in place and discuss next steps in the near future.”

Born in Upper Darby and raised in Broomall, Mr. Cellucci put himself through college working at the Breyer’s Ice Cream Factory, graduating from St. Joseph’s University in 1976 and Georgetown Law School three years later.

Mr. Cellucci spent his entire professional career at White & Williams. He started at the firm in 1979, when it had 55 lawyers — almost half worked on insurance defense litigation. Now the firm has 230 lawyers and less than a third work on insurance defense matters.

During a 2010 interview, Mr. Cellucci said he started out handling white-collar defense and class-action defense work for partner Ted Flowers. But when Flowers died from cancer in 1983, Cellucci made the transition into insurance coverage work, which was a small practice at the firm that he grew over time. He particularly focused on those cases involving environmental liabilities. He said the group took off in the 1980s as asbestos-related litigation rose.

One of his first cases involved the Township of Jackson Landfill in which he successfully represented Cigna Corp., leading to a landmark decision that involved fear of cancer claims and medical monitoring. He devoted over two decades of his professional energies to resolving issues concerning the Township of Gloucester/GEMS Landfill, including the creative implementation of the first private party Superfund contribution procedure.

Mr. Cellucci had success in representing Cigna and Ace. Ltd. in insurance coverage matters for over three decades. One of his most recent successes before the Supreme Judicial Court of Massachusetts, where a landmark 2009 ruling in favor of the insurance industry on the allocation of long-standing environmental pollution was issued.

At White & Williams, he became a partner in 1987, executive committee member in 1994 and commercial litigation department chairman in 1999.

Mr. Cellucci’s colleagues said he would strategize on cases even if he was not involved in them and would mentor younger attorneys.

“He was always willing to discuss anything that was on someone’s mind, personal or professional; he always made time,” White & Williams reinsurance practice chairman Michael Olsan said “He was like a big brother to me.”

Outside of work, Mr. Cellucci enjoyed spending time in Avalon, N.J., golfing whenever possible, and was an avid Philadelphia Eagles and Penn State football fan. He supported La Salle Academy and was affiliated with St. Patrick’s Church.

"He was an immensely talented, yet humble individual with a courageous desire to make the world a better place for his work associates, friends and family," Dan Cellucci said. "We will all miss him dearly."

Relatives and friends are invited to his viewing Thursday, November 21, 2013 6:00-9:00 p.m. and Friday, November 22, 2013 9:30-10:30 a.m. at SS Simon & Jude Church, Route 352 and West Chester Pike, West Chester. His funeral mass will follow at 10:30 a.m..